In recent years, with the great progress of mobile telecommunication, digital mobile products of all kinds, such as mobile phone, laptop, PDA and so on have been the important part of human daily life. Therefore, the requirements of the wireless Internet such as receiving/sending e-mail immediately and obtaining real-time information are increasing vastly. And how to connect the wireless telecommunication with the Internet thereof becomes an important research topic in nowadays. Please refer to FIG. 1, which is a schematic diagram showing the wireless Internet scheme. To get resources in the Internet, the user needs a point-to-point link to download and upload information. In fact, from the viewpoint of the wireless Internet, a point-to-point link can be divided into two parts: the wireless telecommunication from the mobile unit to the base station, and the network communication from the base station to the Internet. Wherein, in the part of the wireless telecommunication, the data will be transmitted from the mobile product to the base station and received from the base station via wireless. It's a direct point-to-point connection. However, in the part of the line network connection, the data are transmitted to the Internet via the present framework such as telephone network and optical fiber communication, and then sent to the remote terminals such as server, personal computer, work station and so on. The network connection needs more network control information for each of the connections.
In fact, the most common point-to-point transmission protocol in the Internet is the Transmission Control Protocol/Internet Protocol (TCP/IP), which is built in the traditional point-to-point transmission protocol of network connection. For its excellent reliability as well as robustness and the growth of Word Wide Web (WWW), the TCP/IP has been utilized extensively in the Internet now.
In the traditional network connection, if the transmitted data are larger, they will be divided into several smaller portions to avoid occupying too much frequency bandwidth in each transmitting, and then transmitted successively in the packet format; finally, all the packets will be received and combined by the remote receiver. However, because the networks are extended in all directions and the network statuses are instantaneously varying, the paths of packets may be different, and thus the received sequence may be different from the original transmitting sequence. Therefore, to avoid confusing the packet sequence and to recombine all the packets correctly, we need to define certain labels on such packets, which are so-called “header”. Please refer to FIG. 2, which shows the header format in typical TCP/IP packet of the prior art. The TCP/IP header can be divided into two pans: the Transmission Control Protocol (TCP) header and the Internet Protocol (IP) header.
The IP header comprises a Version field, which has 4 bits to label the using version of the TCP/IP; an Internet Header Length (IHL) field with 4 bits for specifying the length of the IP header; a Type of Service field with 8 bits, which relates to the quality service types such as the minimum delay, the maximum throughput, the maximum reliability, and the minimum cost; a Total Length field with 16 bits for indicating the total bits of the package; an Identification field with 16 bits, which gives each package an unique serial number for conveniently recombining the packages from the receiver. Next, the filed provides a 3 bits information flag set, an Indicate flag with 1 bit, a Don't Fragment (DF) flag with 1 bit, and a More Fragment (MF) flag with 1 bit. Wherein the indicate flag, shown as symbol A in FIG. 2, is used to indicate whether the information flag set is triggered; the DF flag, shown as symbol B in FIG. 2, is used to indicate whether the package may be fragmented, and the MF flag, shown as symbol C in FIG. 2, is used to indicate whether the package is the last one. And then, the next field is a Fragment Offset field with 13 bits for indicating the fragment address corresponded to the original location in the data beginning. The IP header also comprises a Time to Live field with 8 bits, which is used to indicate the maximum time the package is allowed to remain in the Internet system; a Protocol field with 8 bits for indicating the Internet protocol type the package is using; a Header Checksum field with 16 bits for detecting whether the package is transmitted correctly; a Source Address field with 32 bits for storing the address of the transmitting terminal; and a Destination Address field with 32 bits for storing the address of the receiver. In summary, the total length of the IP header is 20 bytes.
The TCP header comprises a Source Port field with 16 bits for indicating the working port of the transmitting terminal; a Destination Port field with 16 bits for indicating the working port of the receiver; a Sequence Number field with 32 bits, which corresponds to the sequence number of the package; an Acknowledgment Number field with 32 bits for indicating the sequence number of the package that has been received; a TCP Header Length field with 4 bits for specifying the figure of the TCP header length; a Reserved field with 6 bits, which is not used yet. Next the reserved field are 6 control bits, including an Urgent Flag field (URG), shown as symbol D in FIG. 2, with 1 bit for indicating whether the package carries the urgent data; an Acknowledgment Flag field (ACK), shown as symbol E in FIG. 2, with 1 bit for indicating whether the package asks the response form the receiver; a Push Flag field (PSH), shown as symbol F in FIG. 2, with 1 bit for indicating whether the package pushes the receiver to send the data to the application program; a Reset the Connection Flag field (RST), shown as symbol G in FIG. 2, with 1 bit for indicating whether the data needs to be resent; a Synchronous Flag field (SYN), shown as symbol H in FIG. 2, with 1 bit for indicating whether the synchronization needs to be carried out; a Finish Flag field (FIN), shown as symbol I in FIG. 2, with 1 bit for indicating whether the transmission is over. After these control bits is a Buffer Length field with 16 bits, which is used to indicate how much free space is remained so as to avoid the error of Overflow. The TCP header also has a Checksum field with 16 bits for detecting whether the package is transmitted correctly and an Urgent Pointer field with 16 bits for storing the urgent data when the URG control bit is set. In summary, the total TCP header is of 20 bytes. And basically, the length of TCP header is a multiple of word.
From the foregoing, the total length of general TCP/IP header is 40 bytes. That is, each packet needs to increase the transmission amount of 40 bytes, which is very bulky and wasted, and thereby several new header compression formats are continually brought out to solve such problems. In the traditional network connection, the most common header compression method is Van Jacobson TCP/IP header compression, so-called RFC 1144 compression. RFC 1144 can efficiently compress the header format by eliminating some unvaried fields such as the Version field, the Destination Address field, and the Destination Port field during the lifetime.
In the wireless communication, RFC 1144 is also the most familiar method to compress the headers at the present day. However, it is designed to aim at the traditional network connection structure, not at the wireless telecommunication, so this method does not consider the limitation of the wireless transmission such as the narrower bandwidth. In fact, the major bottleneck of the wireless Internet is the part of the wireless communication, so how to increase the efficiency of the data transmission has become a very important topic now. In the wireless communication, each unnecessary data transmitting will reduce the substantial transmission rate; therefore, if we can utilize some characters of wireless telecommunication to carry out the further data compression, the data transmission rate will be improved largely.